INTERNATIONAL Journal of 3 R’s Jan – Mar 2013 INTERNATIONAL Vol. 4, No. 1, 2012, 520-533 Journal of 3R’ s PHOTOCATALYTIC COATINGS FOR BUILDING MATERIALS: DEGRADATION OF NOX AND INHIBITION OF ALGAL GROWTH Thomas Martineza, b, Deborah Dompointa and Alexandra Bertrona*, Gilles Escadeillasa, Erick Ringota, b a Université de Toulouse; UPS, INSA; LMDC (Laboratoire Matériaux et Durabilité des Constructions); 135 avenue de Rangueil; 31 077 Toulouse Cedex 04, France b LRVision SARL - Zi de Vic, 13 rue du Développement - 31320 Castanet-Tolosan – France ABSTRACT The objective was to confer photocatalytic properties on building materials in order to reduce air pollution and to limit algal growth on concrete walls. TiO 2 photocatalytic particles were incorporated in polymer-based glazes (varnish-type coatings). Glazes were formulated with organic solvent-free compounds in order to minimise the toxicity of the inal product. Glazes were applied to mortar substrates. The eficiency of the glaze was tested on nitrogen oxides, representative of indoor and outdoor air pollution, using a laboratory experimental low-type reactor. Commercially available TiO 2 photocatalysts active under UV light and under visible (vis) light were used and tested to investigate the eficiency of the NOx abatement in outdoor and indoor lighting conditions respectively. The glaze incorporating UV-activatable TiO 2 was found to be more eficient than the vis-activatable TiO 2 . Resistance to wet abrasion of the coating, assessed by measuring the NOx degradation over progressive abrasion cycles, was found to be satisfactory, the performance being maintained over the cycles. Biological growth inhibition was tested on chlorella algae, an easy to grow algal species regularly mentioned in the literature. Algal growth testing was performed using an accelerated run-off test under outdoor lighting conditions with UV-active TiO 2 glaze. The performance was evaluated using image analysis (area covered and intensity of fouling). No slowdown of the biological growth kinetics could be attributed to photocatalysis. Nevertheless, algal growth slowed signiicantly for mortars impregnated with a water-repellent preparation. Keywords Photocatalysis, Glaze, Nitrogen Oxide, Biological stains, Walls, Air pollutant in urban areas, pollution concentration levels are very similar inside and outside and can reach up to one ppm [1, 2] In addition to the environmental and health issues, there is also economic concern as the treatment of pollution related diseases (ranging from simple irritation to cancer) involves significant cost [3,4]. 1.0 INTRODUCTION The subject of photocatalysis has attracted considerable interest in recent years, as it presents a high potential solution for the treatment of organic pollution – whether of gaseous, aqueous or biological nature. Moreover, this process does not rely on any specific energy supply, since its implementation requires only a photocatalyst (semiconductor) and a light source with sufficient energy. On the other hand, aesthetic deterioration of the external concrete walls of buildings notably results from development of biological stains. The durability of the aesthetic aspect of buildings is economically important since it conditions the frequency and cost of facade renovation. The stains are linked with the growth of various microorganisms (algae, fungi, mosses), microscopic algae being the pioneer organisms responsible for the first visible stains on facades [5]. Traces have various colours (black, green, red, etc.) and may spread over the whole frontage [6]. It generally takes a year for stains to appear on walls but, with favourable growth conditions (mainly related to humidity, temperature and luminosity, [5]), development can be extremely rapid [7]. Different types of preventive or curative treatments exist, but they generally involve biocidal products [8] that can be detrimental to the environment. Thus, eco-friendly solutions should be found. The aim of this study was to confer some photocatalytic properties on some surfaces of a building in order to (i) reduce gaseous pollution indoors and outdoors and (ii) protect facades against algal proliferation. On the one hand, air pollution mainly results from anthropogenic activities that are sources of emission of a large number of polluting compounds proven to be detrimental to health. For example, urban areas are highly polluted with nitrogen oxides (NO X = NO + NO 2) produced by intensive human activity, notably transport. In housing, NO X are produced by domestic combustion devices such as gas burners for cooking and by the infiltration of outdoor pollution. Actually, *Corresponding author Tel : + 33561559931 E-mail : bertron@insa-toulouse.fr 520 INTERNATIONAL Journal of 3 R’s The photocatalysis process is based on the irradiation of semiconductor materials — generally anataseTiO 2 particles — with high - energy photons that raise electrons, i.e. e –, from the valence band to the conduction band, thus leaving electron holes, i.e h+, (reaction 1). The pairs of mobile charges produced can reach the surface of the semiconductor particle and initiate a reduction - oxidation process. Moreover, through reactions with the oxygen and water adsorbed from the surrounding air, reactive oxygen species such as HO ● and O2●— are created (reactions 2, 3) and act as strong oxidants with the potential to decompose or mineralise a wide range of compounds [9, 10]. After a complete photocatalytic reaction on organic compounds, the end products should theoretically be carbon dioxide and water (mineralisation). TiO 2 hv H 2 O ads + h + (O 2) ads + e– • • + vb + However, despite these biocidal and self-cleaning properties, few studies concern the application of photocatalysis as a preventive treatment against biofouling of construction materials. Gladis and Schumann [26] studied the development of chlorella, stichococcus and coccomyxa on photocatalytic glass plates. The growth of algae in an atmosphere of saturated humidity under different types of illumination (visible light alone, mix of visible light and UV-A) was not impacted by the phenomenon of photocatalysis although the oxidative nature of the material had been validated by the degradation of methylene blue dye. Moreover, measurements of the cells’ permeability on coated and uncoated materials showed no significant differences. However, in another work [27], the same authors observed an inhibition of growth of the algae stichococcus by photocatalysis using a filter on which a suspension of ZnO had been dried. Similar results were obtained by De Muynck et al. on aerated concrete specimens coated with TiO 2 exposed to cyclic water run-off [28]. In a similar experiment, no visible algal growth was observed on a cement paste prepared with commercial TiO 2 -bearing cement, whereas laboratory-made photocatalytic cement (containing 5 and 10% TiO 2) did not appear to be efficient to avoid algal growth [29]. Outdoor weathering over several years showed that photocatalytic coating on roof tiles was not effective against phototrophic growth [30]. The activation of TiO 2 photocatalyst requires UV light (ƛ < 388 nm, band gap energy of 3.2 eV), which is almost absent in indoor environments. For indoor air purification, two methods are employed to make the photocatalyst active under visible light. One involves chemical modifications of the UV active photocatalyst in order to enlarge the photoadsorption to the visible region of the spectrum and to make it efficient in indoor environments. Some studies have focused on the development of photocatalysts active under visible light. For example, carbon-doped TiO 2 , BiOBr or PbWO 4 have shown NOx purification abilities under visible light [11–13]. Although several studies have shown that NOx removal by UV-activatable TiO 2 is possible and provides interesting degradation ratios [14–19], the efficiency of visible light-activatable photocatalysts in indoor light conditions has been studied far less. Published works have shown that doped TiO 2 can degrade some VOCs when activated by visible fluorescent lamps or blue LEDs [12, 20]. Regarding colonisation by microorganisms, TiO 2 photocatalysts have been found to kill bacteria, viruses and algae under UV illumination [21–23]. On the basis of studies on the photokilling of escherichia coli cells in suspension pipetted onto TiO 2 coated glass, Sunada et al. proposed a three-stage mechanism for the degradation of microorganisms on illuminated TiO 2 [21]: • photocatalysis (OH●, H2O2, O2●–); Destruction of the cytoplasmic membrane causing death of the cell; Decomposition of the dead cell. Additionally, surfaces containing TiO 2 as a photocatalyst can have superhydrophilic properties under UV illumination [24, 25]. This phenomenon reduces the contact angle of a drop of water to near zero. When the surface is tilted, the water ilm thus formed falls by gravity (or easy rinsing) removing the accumulated dirt and the products of the photocatalytic reaction. The photoinduced superhydrophilicity of TiO 2 combined with the degradation of organic pollutants by photocatalysis can therefore give a surface with selfcleaning properties. e–cb ––––––––––––– (Eq. 1) H+ + HO • ––––––––––––– (Eq. 2) O 2 •– –––––––––––––––––––– (Eq. 3) TiO 2 + h Jan – Mar 2013 In this paper, commercially available TiO 2 active (i) under UV light, or (ii) under visible light was used. The photocatalyst was incorporated in a glaze. A glaze is a kind of ultra-light varnish. This type of coating was chosen for its architectural interest: it allows the treatment of existing surfaces while maintaining their original appearance. In addition, although many Creation of defects in the outer membrane of the cell by the reactive oxygen species generated by 521 INTERNATIONAL Journal of 3 R’s The mortars intended for algal colonisation were cast in 5X5X0.5 cm 3 PVC moulds sprayed with demoulding oil and subjected to about ten shocks (by gravity) to help the mortar fill the mould properly. The moulds were then put in a storage room (100% relative humidity and temperature 21°C) for 24 hours. After demoulding, the mortar specimens were stored in a room with a regulated atmosphere (20°C, 50% RH) for 15 days. The mortar specimens intended for algal colonisation tests were then kept in an accelerated carbonation chamber (50% air, 50% CO 2 , RH in the 60%–70% range) until complete carbonation was obtained (1 month). This carbonation period was necessary to reduce the pH of the mortar substrate before algal inoculation (initial pH of cementitious materials, around 13, inhibits algal growth). photocatalysis applications for building materials involve TiO 2 incorporated in the matrix of the material (concrete, mortars) during manufacturing [16,31– 35], a coating enables the amount of photocatalyst to be optimized since photocatalysis is a surface phenomenon. The efficiency of NOx removal of the photocatalytic glazes was tested under outdoor and indoor lighting conditions. The influence of humidity and pollutant concentration on the performance of the glaze was evaluated. The durability of the coating was also investigated by measuring the NOx removal performance of the glaze after cycles of mechanical abrasion. The efficiency of the UV-activatable photocatalytic glaze against algal growth proliferation on mortar substrates was tested using Chlorella algae in laboratory conditions. Moreover, another type of preventive treatment against algal colonisation was tested by impregnating the substrate with water repellent compounds. The mortars intended for air purification experiments were cast in 30 x 30 x 1 cm 3 steel moulds. The resulting slab was then sawn into 5 x 10 x 1 cm 3 samples. After demoulding, the mortar specimens were stored in a room with a regulated atmosphere (20°C, 50% RH) for 28 days. 2.0 EXPERIMENTAL The photocatalytic coatings were applied to the cast plane surface of the mortars using a brush. The amount of coating deposited was about 80 g m –2 (determined by weighing). 2.1 Materials Two types of treatment were studied: For the water repellent treatment, the product was applied until all open superficial pores were saturated. Photocatalytic glazes were formulated using silicate/ acrylic-based binders. Water was used as the solvent to limit the use of hazardous chemical products. Thickeners and wetting agents were also incorporated to ensure good wettability and uniformity of aspect of the coating. Two types of commercial TiO 2 photocatalysts were used depending on the application envisaged (outdoor/indoor) : • • • Jan – Mar 2013 Some control specimens, mortar prisms free of any coating, were also tested. 2.2 Degradation of NOx gas The schematic diagram of the experimental set-up used for the study of NOx degradation is presented in Figure 1, and has been fully described in another paper [19,36]. This device comprised of a system generating a polluted air low obtained by diluting a standard source (Air Liquide) with air from a generator (Environment SA, model ZAG7001). The low was then directed either to a reactor (cylindrical borosilicate-glass reactor used for its high transparency to UV-A and its low adsorption capacity, (Figure 2) where the photocatalytic reactions took place, or to a secondary line (bypass) for veriication of the input parameters. The air low was controlled by three mass low controllers (Bronkhorst) that adjusted the dilution ratio of the standard gas, the low rate into the reactor and the humidity level by passing the gas through a bubbler. The UV-activatable TiO2 was a commercial slurry solution available from Millennium Chemicals (S5300B). This glaze does not alter the aesthetic aspect of the surface and contains 2% wt TiO2 The visible-light-activatable TiO 2 was KRONOS VLP7000 (carbon-doped C-TiO 2) in the form of a dry powder. The formulation contained 10% photocatalyst and 10 2 pigmentary grade TiO 2 (Coloris-gcc) resulting in a white painted surface after treatment of the sample. A water repellent impregnation was formulated using silane and luorinated compounds (only tested in the algae colonisation test). The reactivity of the oxygen species generated by the activation of the photocatalyst led to the oxidation of NO to NO2 which, in turn, produced nitrite and nitrate ions NO2 -/NO3 - [19,37–39] (Eq. 4). These coatings were applied to hardened CEM I cement mortars with water to cement ratios of 0.5 for NO X degradation testing and 0.7 for algal colonisation tests. The formulation and manufacturing of the mortars was adapted from the NF EN 196-1 standard. Two types of mortar specimens were manufactured: NO 522 HNO2 NO 2 HNO3–––––––––––––––––––(Eq. 4) INTERNATIONAL Journal of 3 R’s analyser in order to adjust the concentration of NO to the target value using the mass low controller. Once the measured concentration was stable, gas was allowed to pass through the reactor. 10 1 3 5 6 The photocatalytic performance of the various samples was assessed by three conversion ratios calculated as follows: 7 3 Jan – Mar 2013 8 9 4 3 CR NOX (%)= CR 2 NO (%)= Figure 1. Schematic diagram of the experimental apparatus for NO degradation. (1) Zero air generator; (2) NO source; (3) Thermal mass low controller; (4) Gas washing bottle humidiier; (5) Mixing chamber; (6) Temperature and relative humidity probes; (7) Reactor cell; (8) NOx analyser; (9) Bypass; (10) Illuminant CR No2 (%)= [NOX]in – [NOX]out X 100 –––––––––––––––––––––(Eq. 5) [NOX]in [NO]in – [NO]out [NOX]in X 100 –––––––––––––––––––––(Eq. 6) [NO2]in – [NO2]out X 100 –––––––––––––––––––––(Eq. 7) [NOX]in where [NOX]in , [NO]in and [NO2]in are the inlet concentrations of the gases in the experimental procedure and [NOX]out, [NO]out, [NO2]out are the average outlet concentrations measured in the last 30 minutes of a one-hour illumination period. The experimental conditions were as follows: low rate 1.5 l min-1; initial NO concentration 400 ppb; humidity 6g kg-1 (corresponding to 31% RH at 25°C). Several measurements in the conditions ixed above showed a standard deviation of the NOX degradation rate of 0.9% on seven different coated mortar samples and of 3.6% on seven different coated glass samples. In order to investigate a possible photolysis phenomenon (degradation of NO caused directly by the light), control experiments were performed using mortar substrate without photocatalytic coating exposed to the illumination used in the whole study. The removal rate of NO in this condition was almost zero, which proved that no photolysis of NO occurred. Figure 2. Borosilicate-glass reactor (diameter = 60 mm, length = 300mm The concentrations of NO and NO 2 gases were measured with a chemiluminescence analyser (Environnement SA, AC32M) with a detection limit of 0.4 ppb and a continuous sampling rate of 0.7 litre per minute. NO and NO X concentrations were measured in successive, 5 second steps. The NO 2 concentration was obtained from the difference between the NO X and NO concentrations. 2.3 Durability Experiments The durability of the photocatalytic glaze was assessed by measuring the NO X abatement performance of the coating over wet abrasion cycles applied to the coated mortars using an automatic abrasion scrub tester (Elcometer 1720, standard ASTM D2486 [41] Figure 3). The photocatalytic activation of the samples intended for outdoor applications (NOX abatement by UVactivatable TiO 2) was carried out using a 300-W OSRAM Ultra Vitalux bulb with an emission spectrum close to that of daylight. The light intensity measured using a UV-A radiometer (Gigahertz-Optik) was 5.8 W.m– 2 , which corresponds to lighting conditions encountered on a cloudy day [19]. Liquid flow-control valves Carriage For formulations intended for indoor use, testing was performed using a fluorescent lamp (in accordance with draft standard ISO 14605 [40]). For some tests of NOx abatement by the C–doped TiO 2 glaze, the lamp was fitted with an acrylic filter (OP3 filter) to ensure the elimination of the UV portion of the lamp spectrum. The light intensity measured using a radiometer (Gigaherzt Optik, X11) was 730 mW/m 2 in the 400-500 nm range and 1590 lux. Specimen holding frame Holding frame clamp Figure 3. Principe of abrasion test equipment (Elcometer 1720) After 1000 abrasion cycles using a nylon brush, the coated mortars were rinsed with tap water and Prior to the UV illumination period, NOx-contaminated air was passed in the dark through the bypass directly to the 523 INTERNATIONAL Journal of 3 R’s wiped using absorbent paper and the NO X abatement performance of the specimen was then assessed using the experimental set-up and procedure described in section 2.2 of this paper. Jan – Mar 2013 closed pumps ensured constant movement and mixing of the medium. The prisms were inoculated through the run-off. 2.4 Algal Growth 2.4.1 Accelerated Colonisation by Water Run-off In order to accelerate algal growth on mortar specimens, the water run-off dynamic test set-up developed by Escadeillas et al. [5, 42] was used and adapted to this study. The device was inoculated using Chlorella algae (Chlorophyceae class) as this species is representative of species regularly referred to in the literature, and is easy and rapid to grow [5]. The device (Figure 4) consisted of a transparent polycarbonate chamber (1X0.5X0.5m3) divided into 4 alveoli, each containing a 45° tilted support for the mortar prisms under test. This chamber, itted with a lid, was stored in an air-conditioned room (21°C) where no outside light could penetrate. The photocatalytic particles used in the glaze being activated by the UV part of the solar spectrum, and the growth of algae and cyanobacteria being essentially dependent on visible light (red and blue in particular), the chamber was itted with a “full-spectrum” luorescent tube (ARCADIA Natural Sunlight®) and a UV-A tube (Sylvania®). These tubes illuminated the mortar prisms and the culture medium containing algae to ensure their development (Figure 4) [b]. Pumps and watering ramps allowed algal growth medium (BG11) to low over the sample surface. The imposed photoperiod was 12 h day and 12 h night. The run-off was set at 1 h per day. It was ensured by immersed pumps (300 l/h aquarium-type pump) connected to spraying ramps. The liquid from the spraying ramps irst fell on PVC prisms situated above the mortars under test and having the same size. 10 l of algal growth medium was placed in each of the alveoli. A circuit of immersed, Figure 4. b) Top view of the run-off test (adapted from Escadeillas [5] 2.4.2 Light Conditions UV light intensity in the chamber had to be representative of the exposure of a facade in a real situation. High UV intensity could lead to the eficiency of photocatalysis activity being overestimated and could alter microorganisms by photochemical effects (molecular, cell or physiological damage [43]). The intensity of UV-A light from the sun is in the 6-30 W.m–2 range depending on the sunlight conditions [19, 44, 45]. Irradiance was measured at the mortar surface in the 310-400 nm (UV light) and 400-500 nm (visible light) ranges using a radiometer (Gigahertz-Optik X11) at the different zones inside the chamber. UV lamp Full spectrum lamp Watering system PVC prisms Sample Water (+Bg11) + algae Pumps Figure 5. Distribution of UV-A (310-400 nm) and visible light (400-500 nm) in the run-off test Figure 4. a) Schematic diagram of water run-off dynamic test set-up 524 INTERNATIONAL Journal of 3 R’s Because of the difference of luminosity between the centre and the sides of the tube, different illumination conditions were available in the test set-up. The irradiance measurements indicated four zones of different UV light conditions: 12, 7.5, 3, 1.5 W.m–2 for zones 1 to 4 respectively (Figure 5). For visible light, measurements in the 400-500 nm range showed two zones with different intensities: one at the centre of the luorescent tube with 0.9 W.m–2 and the other at the ends with 1.5 W.m–2 . 2.4.3 Quantiication of Growth using Image Analysis Image Acquisition During colonisation by algae, the surfaces of the mortars were photographed using a scanner (EPSON Perfection 2580) at a resolution of 600 dpi. This device is suitable for image analysis because it ensures reproducible conditions of light and image size. Before each acquisition, samples were stored for 3 hours in the atmosphere of the room in order to avoid any inluence of moisture on the grey level. Image Processing The colour of each pixel of the photograph was characterized by 3 coordinates in the RGB colorimetric space (R: red, G: green, B: blue). The irst step of the analysis was to convert the image into grey levels using equation (1): Grey = 0.299 Red x 0.587 Green x 0.114 Blue –––––(Eq. 8) The coeficients in reaction (Eq. 7) (the sum of which is 1) account for the way the human eye perceives red, green and blue colours (recommendation 601 of the International Commission on Illumination, CIE). New pixels are characterized by one component, the value of which indicates the grey level over 256 values from white (255) to black (0). When the image is converted into grey levels, the zones with most intensive colonisation are characterized by a grey level close to black (Figure 6). Jan – Mar 2013 Colonized Area The “K-Means-like” method was used for the quantiication of the area colonized by algae [42]. This algorithm performs an automatic classiication that partitions the image in the parameter space (RGB) into a given number of classes. In the case of colonized surfaces, the K-means-like method allowed greenish pixels representing algae to be grouped separately from the grey ones of non-colonized zones. Quantiication was performed with a separation into three classes. After identifying the classes belonging to the colonized area by comparison with the image areas that kept their original colour, the area colonized was determined by calculating the percentage of pixels colonized. Intensity of Fouling To evaluate the intensity of colonisation, pixels were sorted into eight classes according to grey level and then counted. This method gave the area occupied by algae at various intensities of colonisation and thus the total colonized area of each sample. Figure 7 shows the distribution of pixels in the eight classes of a 5X5 cm2 mortar specimen during the progression of colonisation of the sample. The image of the non-colonized specimen is mainly composed of Class 5 and Class 4 pixels. The progression of colonisation is accompanied by the darkening of the image and thus by the increase in number of pixels in classes 0-4. When colonisation becomes total and intense, the image tends to be composed exclusively of pixels of class 0. The colonisation index I (%) was determined as follows: I(%) = 100 – 100 x with 800 – Ct ––––––––––––––––––––––(Eq. 9) 800 – Ct = O 0 1 2 3 Ct = 8 x Ct + 7 x Ct + 6 x Ct + 5 x Ct + 4 x––––––(Eq. 10) Where Ct is the intensity of the colonisation level after t days of test and Ctn is the percentage of pixels in class n after t days of test. The results of discrimination of colonisation intensity levels were similar in significance to those obtained using reflectance measurements with a spectrophotometer [5, 42, 46]. The present method allowed the heterogeneity of the intensity of development to be better taken into account than the reflectance measurements since the analysis was performed at pixel scale whereas a spectrophotometer measures on an area between 50 and 490 mm 2 depending on the characteristics of the device. Figure 6. Conversion of the image of a colonized mortar specimen into 8 grey levels 525 INTERNATIONAL Journal of 3 R’s Jan – Mar 2013 3.0 RESULTS 100 Occupied area (%) 80 3.1 NOX Abatement Performances 60 3.1.1 Comparison of Performances of UV- and 40 Vis-activatable TiO2 Glazes 20 0 0 1 2 3 4 5 6 7 Pixel class I(%)=0% Occupied area (%) 100 80 60 40 20 0 0 1 2 3 4 5 6 7 Pixel class I(%)=15% For an initial NO concentration of 400 ppb, Figure 8 shows the changes in concentrations of nitrogen oxides obtained with the C-doped photocatalytic coatings applied to mortar under (i) a UV/Visible light irradiation (full spectrum lamp) (left) and (ii) a visible light irradiation (luorescent lamp with UV ilter) (right). The irst step of the experimental procedure was performed in darkness. The gas was made to pass through the bypass directly to the analyser in order to adjust the concentration of NO to the target value using the mass low controller. Once the measured concentration was stable, gas was allowed to pass through the reactor. The concentration decreased immediately because of the illing time of the cell and adsorption on surfaces. After saturation, the NO concentration returned to the initial value and photocatalytic reactions were then initiated by switching on the lamp (19). 80 Concentration (ppb) Occupied area (%) 100 60 40 20 0 0 1 2 3 4 5 6 7 Pixel class 0 I(%) = 78% Concentration (ppb) Occupied area (%) 100 80 60 40 20 0 12 3 4 56 7 Pixel class I(%) = 89% 100 80 60 40 20 0 0 12 3 4 56 7 Pixel class I(%) = 100% Figure 7. Evolution of the area occupied by the 8 pixels in classes based on the colonisation status of the sample 20 40 Time (minutes) 60 450 400 350 300 250 200 150 100 50 0 0 0 Occupied area (%) 450 400 350 300 250 200 150 150 50 0 10 20 30 Time (minutes) 40 50 Figure 8. Degradation of NO by C-doped TIO2 photocatalytic coatings immobilized on mortar substrate (initial NO concentration = 400 ppb, Q = 1.5 L.min- 1 , H = 6 g.kg- 1). Left: full spectrum lamp (UV-visible light irradiation), Right: luorescent lamp with UV ilter (visible light irradiation only). In the conditions of the test, the UV-A radiation measured under the luorescent lamp was 270 mW/m2 without the ilter and 73 mW/m2 with the ilter. Under the full spectrum lamp, the UV-A radiation was 5800 mW/m2. Irradiance measurements were carried out at several locations in a typical ofice room itted with luorescent lamps (20 measurement points regularly spaced 1.2 m apart and at 1.7 m height). It was found that: (i) the average intensity was 110 ± 12 mW.m–2 for UV-A and 300 ± 120 mW.m–2 for visible light with indoor lighting only (closed shutters) 526 INTERNATIONAL Journal of 3 R’s and that (ii) the average intensity was 160 ± 18 mW. m–2 for UV-A and 500 ± 320 mW.m–2 for visible light with additional outdoor lighting (open shutters). the performances of vis-activatable photocatalytic coatings under indoor lighting conditions (luorescent lamp with or without UV ilter) were far lower than UVactivatable photocatalytic coatings under full spectrum light (outdoor lighting conditions). Moreover, it should be noted that the conventional TiO2 glaze was more eficient under the luorescent lamp without UV ilter than the C-doped TiO2 glaze was. Figure 9 shows the NO and NO X conversion ratios of the doped and conventional photocatalysts alone (deposition of powders on the mortars) under various lighting conditions. Degradation rate (%) 50 45 Figure 10 shows that the presence of a binder greatly reduced the conversion ratios compared to TiO2 photocatalysts alone. However, despite the barrier effect of the binder, the air puriication properties of the glazes under visible light were veriied. Improvements must now be made in the design of visible light activated photocatalysts on the one hand and in the glaze formulations on the other. 40 35 30 25 20 NO 15 10 5 0 NOx TiO2 C-TiO2 TiO2 C-TiO2 Full spectrum lamp Fluorescent lamp with UV-filter TiO2 Jan – Mar 2013 C-TiO2 However, since the conversion ratios obtained using a low type reactor are highly dependent on the experimental conditions and on the design of the reactor (residence time of the polluted air, initial pollutant concentration and geometry of the reactor), the air puriication performance of the resulting optimized formulation should be evaluated under real conditions. Fluorescent lamp without UV-filter Figure 9. NO and NOx degradation rates of the photocatalysts alone (conventional TiO2 and C-doped TiO2 without binder) under full spectrum lamp (UV-visible), luorescent lamp with UV ilter (visible light only) and without UV ilter. 45 40 Conversion ratios (%) Deposition of C-TiO2 without binder on the mortar substrate led to conversion ratios of 7.3% for NOXCR and 11.8% for NOCR under visible light alone (with UV ilter). Under full spectrum lamp and under luorescent lamp without UV-ilter, the eficiency of the conventional TiO2 was very close to that of the C-doped TiO2 . However, in the case of the luorescent lamp with UVilter, the C-TiO2 glazes was three times as eficient (NOXCR = 7.3%; NOCR = 11.8%) as the conventional TiO2 (NOXCR = 2.5% ; NOCR = 2.8% ). Moreover, the results of the experiments performed with low UV irradiance (luorescent lamp without UV-ilter), corresponding to a typical indoor illumination, showed a signiicant increase in the conversion ratios for the two types of TiO2 . 35 NO 30 NOx 25 20 15 10 5 0 TiO2 C-TiO2 Full spectrum lamp TiO2 C-TiO2 Fluorescent lamp with UV-filter TiO2 C-TiO2 Fluorescent lamp without UV-filter Figure 10. NO and NOx degradation rates of the photocatalytic glazes (conventional TiO2 and C-doped TiO2) under full spectrum lamp (UV-visible), luorescent lamp with UV ilter (visible light only) and without UV ilter. Figure 10 shows the NO and NOX conversion ratios of the coatings formulated with non-doped photocatalyst TiO2 and with carbon doped TiO2 (C-TiO2) under various lighting conditions. 3.1.2 Inluence of Abrasion on Degradation Rates Figure 11 shows the inluence of wet abrasion cycles on the NOx abatement performances of the glazes applied to mortars. Experiments were performed under UV/ Visible irradiation (sunlight simulation) and under pure visible light. Figure 10 shows that: (i) both TiO2 and C-doped TiO2 are eficient under full spectrum light, but C-doped TiO2 (NOCR= 29%) is some what less eficient than conventional TiO2 (NOCR = 40%) in the case of the formulation studied, (ii) conventional TiO2 is hardly eficient under visible light alone which supports experiments performed on the photocatalyst alone, the degradation rates being very low (NOCR = 2% and NOxCR = 1.5%), (iii) C-TiO2 glazes are more eficient than conventional TiO2 glazes under visible light alone with NOCR = 7% and NOXCR=5%. Without the UV ilter, the performances of the C-doped TiO2 glazes under the luorescent lamp were slightly improved (NOCR = 9% and NOxCR = 7%). Nevertheless, Under UV/Visible light, after 1000 cycles of abrasion using a nylon brush, the NOx and NO conversion ratios of the undoped TiO2 glaze, initially 36% and 40% respectively, decreased to 31% and 35% resp. (inlet NO concentration of 400 ppb, low rate of 1.5 l.min– 1). Conversion ratios of C-doped TiO2 were very similar before and after abrasion. In both cases (doped and 527 INTERNATIONAL Journal of 3 R’s Further research on the durability of photocatalytic materials exposed to different environmental conditions is needed. In particular, the inluence of the formulation of the photocatalytic materials (impregnation with TiO2 alone or TiO2 -bearing coating on different building materials) on their durability when exposed to different environments needs to be investigated to optimize the photocatalytic materials. conventional TiO2), the photocatalytic properties were thus maintained despite the abrasion cycles. These results show that a large proportion of the TiO2 particles were still present and active on the substrate after the abrasion [47]. 45 40 NO Degradation rate (%) 35 Jan – Mar 2013 NO x 30 3.2 Algal Development on Mortar Surfaces 25 20 Figure 11 and Figure 12 show the evolution of the colonisation index under two different illumination conditions according to time of exposure in the run-off test. Figure 14 and Figure 15 show the evolution of the colonized area during the run-off test. Finally, Figure 16 shows some pictures of treated (photocatalytic or water repellent treatment) and untreated mortar samples according to time of exposure in the run-off test. 15 10 5 0 1000 cycles 0 cycle TiO2 0 cycle 1000 cycles C-TiO2 Full spectrum lamp 0 cycle TiO2 1000 cycles 0 cycle 1000 cycles C-TiO2 Fluorescent lamp with UV-filter Figure 11. Evolution of NOx/NO conversion ratios of the photocatalytic glazes before and after 1000 abrasion cycles. Values are given for doped and undoped TiO2 under two lighting conditions: full spectrum lamp (UV-visible, 7700 lux and 5.8 W.m-2 UV A) and luorescent lamp with UV-ilter (Visible light only, 1500 lux). The kinetics of the colonisation index and the colonized area progression seemed to be exponential. A latency period was irst observed where no sign of colonisation was detected on the mortars. This latency period lasted between 50 and 100 days depending on the lighting conditions (Figure 12 and Figure 13). The latency period matched the initial growth of the algae in the culture medium circulating in the pumping system and the attachment phase of the algae to the mortar substrate. Then the irst algal stains were detected through image analysis and the evolution was very rapid. The surfaces of the mortar specimens were completely covered in less than 160 days in the most rapid case (Figure 14). When the photocatalysis process was activated by visible light only, conversion ratios were not sensibly altered by the abrasion cycles (NO CR = 7% before abrasion, NO CR = 5.5% after abrasion). To our knowledge, the literature on the durability of photocatalytic materials exposed outdoors is limited [48–52]. The retention of TiO2 particles coated on cementitious materials increases with porosity and roughness [49]. Moreover, laboratory accelerated weathering tests aiming to simulate a typical ageing process on facades (rainy-day and dry-night cycles) show that the photocatalytic properties are maintained even though the physical characteristics of the coating are affected [48, 49]. 3.2.1 Inluence of UV Irradiation UV intensity has a great impact on the development of algal colonisation on mortars whatever the treatment applied. Colonisation on control samples placed under low UV intensities (1.5-3 W.m–2) were detectable earlier than on the samples placed in areas of high UV intensities (7.5-12 W.m–2). Moreover, between 100 and 169 days, the intensity of fouling under radiation, between 7.5 and 12 W.m–2, was half that observed at lower intensity (1.5-3 W.m–2). These results could be explained by a period of acclimation of the algae to UV radiation [43]. The abrasion test set-up used in this study evaluated scrub resistance of the coating under wet conditions (wetting of the specimens was provided by a pump and tap water). The durability of the samples tested may have been due to the presence of a binder and to the penetration of the photocatalytic particles into the surface open porosity and roughness. 3.2.2 Inluence of the Surface Treatment on Algal Development Nevertheless, natural weathering can signiicantly decrease the photocatalytic activity after a few months outside, especially when the material is used as a loor covering. It can also be observed that washing with water alone cannot always completely restore the photocatalytic activity [51–53], which is likely to be signiicantly reduced by the accumulation of oil or grease. In this context, mixing the photocatalyst with an oleophobic compound could improve the durability of air puriication performance. Image analysis did not enable the samples treated with the photocatalytic coating to be distinguished from the untreated samples (Figure 12 to Figure 16). The growth of algae was not reduced by the presence of a photocatalyst in any lighting condition, even the most favourable (7.5 to 12 W.m–2). Similar results were obtained using another test device simulating algal growth at the base of a wall by water capillary ascent [47]. 528 INTERNATIONAL Journal of 3 R’s ascent test. This type of test simulates the moistening of walls at the base of a construction. The duration of the test was 80 days. A single inoculation of the mortar specimens was carried out at the beginning of the test. Untreated control specimens were completely colonized from 45 days [47]. Several hypotheses may explain these results: (i) the development of algae is not affected by the phenomenon of photocatalysis, (ii) the kinetics of algal growth, conditioned by a daily supply of algal cells on the sample surface is greater than the kinetics of cell degradation by photocatalysis, (iii) the development of algae and the residues of dead algae form a barrier to the light needed to activate the photocatalyst. The growth of microorganisms under run-off conditions was not completely prevented in this study. This observation under laboratory conditions supports indings in real situations [8, 54]. Algae could be detected in biological analyzes performed on building material treated with hydrophobic compound (different chemical composition than the water repellent used in this study) and exposed outdoor. The results obtained in the present study clearly show that the bioreceptivity of mortar decrease after the application of the water repellent. Further tests should be carried out under natural weathering to conirm the effectiveness of the protection against microbial colonisation. Nevertheless, it can be observed that water repellent treatment is able to notably slow the progression of colonisation compared to that obtained with the control specimens and photocatalytic samples (Figure 12 and Figure 13). The application of the water repellent reduced the availability of water on the surface of the specimen, and the supply of water is a major parameter of algal growth, together with luminosity, nutrient supplies and temperature [5]. This type of protection also completely prevented the growth of algae on the surface of mortars in tests performed with a BG11 growth medium capillary 100 7.5 - 12 W.m 80 –2 Colonized area (%) Degradation rate (%) 90 70 60 50 Reference 40 30 Photocatalysis 20 Water repellent 10 0 0 50 100 Days of water run-off 150 –2 Reference Photocatalysis Water repellent 50 100 150 Days of water run-off Reference Photocatalysis Water repellent 0 50 100 150 200 Figure 14. Evolution of the colonized area of the samples (UV 7.5-12 W.m–2) 1.5-3 W.m 0 7.5-12 W.m–2 Days of water run-off Colonized area (%) Colonization index (%) 100 90 80 70 60 50 40 30 20 10 0 200 Figure 12. Evolution of the colonisation index of the samples (UV 7.5-12 W.m–2) 100 90 80 70 60 50 40 30 20 10 0 Jan – Mar 2013 200 100 90 80 70 60 50 40 30 20 10 0 1.5-3 W.m Reference Photocatalysis Water repellent 0 Figure 13. Evolution of the colonisation index of the samples (UV 1.5-3 W.m–2) –2 50 100 150 Days of water run-off 200 Figure 15. Evolution of the colonized area of the samples (UV 1.5-3 W.m–2) 529 INTERNATIONAL Journal of 3 R’s Jan – Mar 2013 Figure 16. Macroscopic aspect of mortar prisms exposed to run-off test for different times of exposure (84, 105, 131 and 158 days). Comparison of the algal development between a specimen coated with UV-TiO2 glaze, a specimen coated with a water repellent and a control specimen. The specimens were kept in zone 2 of the run-off test set-up (UV-A: 7.5 W.m–2, VIS: 0.9 W.m–2). should be investigated. The inluence of the formulation of the photocatalytic materials (impregnation with TiO2 alone or TiO2 -bearing coating on different building materials) on their durability when exposed to different environments needs to be known if the materials are to be optimized. 4.0 CONCLUSION Photocatalytic coatings intended for building materials were formulated and tested. Two types of photocatalytic particles were used: conventional TiO 2 nanoparticles activatable under UV light and carbon doped TiO 2 activatable under visible light. The algal growth inhibition performance of the conventional TiO 2 photocatalytic glaze applied to mortar specimens was assessed under a full-spectrum lamp. The development of biofouling was not limited by the photocatalytic treatment. However, the results obtained using the mortars treated with water repellent show that it should be possible to formulate a coating combining hydrophobic and photocatalytic properties to reduce the level of air pollution and to limit the development of microorganisms on buildings. NOx abatement performances of the conventional or C-doped TiO2 glazes were tested under outdoor (full spectrum lamp with high UV intensity) and indoor (luorescent lamp with little UV intensity) lighting conditions. It was found that the performances of the photocatalytic glazes were sensibly lower under indoor lighting conditions than under outdoor lighting conditions. Nevertheless, these irst results on the NOx degradation rates of visible light activatable TiO2 are promising and it may be assumed that more research concerning the design of visible light activated photocatalysts and the formulation of the glazes could improve the air puriication performance of the coatings. Other types of pollutants should also be studied (VOC). The durability of the photocatalytic glazes was also assessed. The NOx abatement performances of the glazes were not much altered after 1000 cycles of abrasion, which showed that there were still suficient amounts of TiO2 particles on the mortar substrate to activate the photocatalysis processes. Nevertheless, the durability of photocatalytic materials exposed to different environmental conditions ACKNOWLEDGMENT The authors thank the ANRT (French Association for Research and Technology), OSEO (French organization supporting research and development), the DGCIS (Direction Generale de la Competitivite de l'Industrie et des Services – French General Directorate of Industry and Services’ Competitiveness) and the Guard Industrie company for their interest and financial support. 530 INTERNATIONAL Journal of 3 R’s [14] Ao CH, Lee SC, Mak CL, Chan LY. Photodegradation of volatile organic compounds (VOCs) and NO for indoor air puriication using TiO2: promotion versus inhibition effect of NO. Applied Catalysis B: Environmental 2003;42:119–29. REFERENCES [1] Jan – Mar 2013 Blondeau P, Lordache V, Poupard O, Genin D, Allard F. Relationship between outdoor and indoor air quality in eight French schools. Indoor Air 2005;15:2–12. [2] Lawrence AJ, Masih A, Taneja A. Indoor/outdoor relationships of carbon monoxide and oxides of nitrogen in domestic homes with roadside, urban and rural locations in a central Indian region. Indoor Air 2005;15:76–82. [15] Maggos T, Bartzis JG, Leva P, Kotzias D. Application of photocatalytic technology for NOx removal. Applied Physics A: Materials Science & Processing 2007;89:81–4. [16] Hüsken G, Hunger M, Brouwers HJH. Experimental study of photocatalytic concrete products for air puriication. Building and Environment 2009;44:2463–74. [3] Jantunen M, Oliveira Fernandes E, Carrer P, Kephalopoulos S. Promoting actions for healthy indoor air (IAIAQ). Luxembourg: European Commission Directorate General for Health and Consumers; 2011. [17] Laufs S, Burgeth G, Duttlinger W, Kurtenbach R, Maban M, Thomas C, et al. Conversion of nitrogen oxides on commercial photocatalytic dispersion paints. Atmospheric Environment 2010;44:2341–9. [4] Krieger P, De Blay F, Pauli G, Kopferschmitt MC. Asthma and domestic chemical pollutants (excluding tobacco). Revue de Maladies Respiratoires 1998;15:11–24. [18] Águia C, Ângelo J, Madeira LM, Mendes A. Photooxidation of NO using an exterior paint - Screening of various commercial titania in powder pressed and paint ilms. Journal of Environmental Management 2011;92:1724–32. [5] Escadeillas G, Bertron A, Blanc P, Dubosc A. Accelerated testing of biological stain growth on external concrete walls. Part 1: Development of the growth tests. Materials and Structures 2007;40:1061–71. [19] Martinez T, Bertron A, Ringot E, Escadeillas G. Degradation of NO using photocatalytic coatings applied to different substrates. Building and Environment 2011;46:1808–16. [6] Perrichet A. Développement de microorganismes à la surface des bétons et enduits. Materials and Structures 1984;17:173–7. [7] Le Borgne A, Lanos C, Trigalleau M. Le bâtiment face à sa microlore. Editions ARIA/INSA 1994:78p. [20] Tseng Y-H, Kuo C-H. Photocatalytic degradation of dye and NOx using visible-light-responsive carboncontaining TiO2. Catalysis Today 2011;174:114–20. [8] Urzi C, De Leo F. Evaluation of the eficiency of water-repellent and biocide compounds against microbial colonization of mortars. International Biodeterioration & Biodegradation 2007;60:25–34. [21] Sunada K, Watanabe T, Hashimoto K. Studies on photokilling of bacteria on TiO2 thin ilm. Journal of Photochemistry and Photobiology A: Chemistry 2003;156:227–33. [9] Hoffmann MR, Martin ST, Choi W, Bahnemann DW. Environmental applications of semiconductor photocatalysis. Chemical Reviews 1995:69–96. [22] Peller JR, Whitman RL, Grifith S, Harris P, Peller C, Scalzitti J. TiO2 as a photocatalyst for control of the aquatic invasive alga, Cladophora, under natural and artiicial light. Journal of Photochemistry and Photobiology A: Chemistry 2007;186:212–7. [10] Blake D. Bibliography of work on the photocatalytic removal of hazardous compounds from water and air: http://www.nrel.gov/docs/fy02osti/31319.pdf 2001. [23] Huang Z, Maness P-C, Blake DM, Wolfrum EJ, Smolinski SL, Jacoby WA. Bactericidal mode of titanium dioxide photocatalysis. Journal of Photochemistry and Photobiology A: Chemistry 2000;130:163–70. [11] Ai Z, Ho W, Lee S, Zhang L. Eficient Photocatalytic Removal of NO in Indoor Air with Hierarchical Bismuth Oxybromide Nanoplate Microspheres under Visible Light. Environmental Science & Technology 2009;43:4143–50. [24] Yu JC, Ho W, Lin J, Yip H, Wong PK. Photocatalytic Activity, Antibacterial Effect, and Photoinduced Hydrophilicity of TiO2 Films Coated on a Stainless Steel Substrate. Environmental Science & Technology 2003;37:2296–301. [12] Yu QL, Brouwers HJH. Indoor air puriication using heterogeneous photocatalytic oxidation. Part I: Experimental study. Applied Catalysis B: Environmental 2009;92:454–61. [25] Diamanti MV, Ormellese M, Pedeferri M. Characterization of photocatalytic and superhydrophilic properties of mortars containing titanium dioxide. Cement and Concrete Research 2008;38:1349–53. [13] Dong F, Huang Y, Zou S, Liu J, Lee SC. Ultrasonic Spray Pyrolysis Fabrication of Solid and Hollow PbWO4 Spheres with Structure-Directed Photocatalytic Activity. The Journal of Physical Chemistry C 2011;115:241–7. [26] Gladis F, Schumann R. A suggested standardised 531 INTERNATIONAL Journal of 3 R’s Jan – Mar 2013 Photobiology A 2000;136:103–9. method for testing photocatalytic inactivation of aeroterrestrial algal growth on TiO2-coated glass. International Biodeterioration & Biodegradation 2011;65:415–22. [38] Dalton JS, Janes PA, Jones NG, Nicholson JA, Hallam KR, Allen GC. Photocatalytic oxidation of NOx gases using TiO2: a surface spectroscopic approach. Environmental Pollution 2002;120:415–22. [27] Gladis F, Eggert A, Karsten U, Schumann R. Prevention of bioilm growth on man-made surfaces: evaluation of antialgal activity of two biocides and photocatalytic nanoparticles. Biofouling 2009;26:89–101. [39] Devahasdin S, Fan C, Li K, Chen DH. TiO2 photocatalytic oxidation of nitric oxide: transient behavior and reaction kinetics. Journal of Photochemistry and Photobiology A: Chemistry 2003;156:161–70. [28] Ramirez AM, De Belie N. Evaluation of the Algaecide Activity of Titanium Dioxide on Autoclaved Aerated Concrete. Journal of Advanced Oxidation Technologies 2009;12:100–4. [40] NF ISO 14605. Avant-projet de norme soumis à enquête publique jusqu’au 16/08/2012. Céramiques techniques — Sources lumineuses destinées aux essais des matériaux photocatalytiques semiconducteurs dans un environnement d’éclairage intérieur n.d. [29] Maury-Ramirez A, De Muynck W, Stevens R, Demeestere K, De Belie N. Titanium dioxide based strategies to prevent algal fouling on cementitious materials. Cement and Concrete Composites 2013;36:93–100. [41] ASTM D2486. Standard Test Methods for Scrub Resistance of Wall Paints 2006:4p. [30] Gladis F, Schumann R. Inluence of material properties and photocatalysis on phototrophic growth in multi-year roof weathering. International Biodeterioration & Biodegradation 2011;65:36–44. [42] Escadeillas G, Bertron A, Ringot E, Blanc P, Dubosc A. Accelerated testing of biological stain growth on external concrete walls. Part 2: Quantiication of growths. Materials and Structures 2009;42:937–45. [31] Poon CS, Cheung E. NO removal eficiency of photocatalytic paving blocks prepared with recycled materials. Construction and Building Materials 2007;21:1746–53. [43] Karsten U, Lembcke S, Schumann R. The effects of ultraviolet radiation on photosynthetic performance, growth and sunscreen compounds in aeroterrestrial bioilm algae isolated from building facades. Planta 2006;225:991–1000. [32] Chen J, Poon C. Photocatalytic Construction and Building Materials:From Fundamentals to Applications. Building and Environment 2009;44:1899–906. [44] Fujishima A, Zhang X. Titanium dioxide photocatalysis: present situation and future approaches. Comptes Rendus Chimie 2006;9:750–60. [33] Strini A, Cassese S, Schiavi L. Measurement of benzene, toluene, ethylbenzene and o-xylene gas phase photodegradation by titanium dioxide dispersed in cementitious materials using a mixed low reactor. Applied Catalysis B: Environmental 2005;61:90–7. [45] Blöß S, Elfenthal L. Doped titanium dioxide as a photocatalyst for UV and visible light. Baglioni P, Cassar L, editors. Proceedings international RILEM symposium on photocatalysis, environment and construction materials, Florence, Italy: Bagneux, France: RILEM Publications; 2007. [34] Demeestere K, Dewulf J, De Witte B, Beeldens A, Van Langenhove H. Heterogeneous photocatalytic removal of toluene from air on building materials enriched with TiO2. Building and Environment 2008;43:406–14. [46] De Muynck W, Ramirez AM, De Belie N, Verstraete W. Evaluation of strategies to prevent algal fouling on white architectural and cellular concrete. International Biodeterioration & Biodegradation 2009;63:679–89. [35] Strini A, Schiavi L. Low irradiance toluene degradation activity of a cementitious photocatalytic material measured at constant pollutant concentration by a successive approximation method. Applied Catalysis B: Environmental 2011;103:226–31. [47] Martinez T. Revetements photocatalytiques pour les matériaux de construction : formulation, évaluation de l’eficacité de la dépollution de l’air et écotoxicité. Université Paul Sabatier, 2012. [48] Maury-Ramirez A, Demeestere K, De Belie N. Photocatalytic activity of titanium dioxide nanoparticle coatings applied on autoclaved aerated concrete: Effect of weathering on coating physical characteristics and gaseous toluene removal. Journal of Hazardous Materials 2012;211–212:218–25. [36] Martinez T, Ringot E, Bertron A, Escadeillas G. Reducing pollution using a photocatalytic lasure. In M El Barrak (ed) Proceedings of the International Conference on Future Concrete 2010. [37] Hashimoto K, Wasada K, Toukai N, Kominami H, Kera Y. Chemistry : Photocatalytic oxidation of nitrogen monoxide over titanium(IV) oxide nanocrystals large size areas. Journal of Photochemistry and [49] Ramirez AM, Demeestere K, De Belie N, Mäntylä T, Levanen E. Titanium dioxide coated cementitious materials for air purifying purposes: Preparation, 532 INTERNATIONAL Journal of 3 R’s Jan – Mar 2013 [52] Yu JC. Deactivation and Regeneration of Environmentally Exposed Titanium Dioxide (TiO2) Based Products. Testing Report, Prepared for the Environmental Protection Department, HKSAR 2003:21. characterization and toluene removal potential. Building and Environment 2010;45:832–8. [50] Hassan MM, Dylla H, Mohammad LN, Rupnow T. Evaluation of the durability of titanium dioxide photocatalyst coating for concrete pavement. Construction and Building Materials 2010;24:1456–61. [53] Beeldens A. Air puriication by pavement blocks: inal results of the research at the BRRC. Transport Research Arena Europe, Ljubljana: 2008. [51] Shen S, Burton M, Jobson B, Haselbach L. Pervious concrete with titanium dioxide as a photocatalyst compound for a greener urban road environment. Construction and Building Materials 2012;35:874– 83. [54] Nugari MP, Pietrini AM. Trevi Fountain: An evaluation of inhibition effect of water-repellents on cyanobacteria and algae. International Biodeterioration & Biodegradation 1997;40:247–53. 533 INTERNATIONAL Journal of 3R’ s Repair, Restoration & Renewal of Built Environment GUIDE FOR AUTHORS Submission of Papers single-column width (i.e. slightly less than halfpage width). For this reason, please keep the blank space around igures and tables to a minimum as this will ensure that the content of igures and tables can be reproduced as large as possible. 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